opposite of << in ruby

Question

I have a huge string being prepared by using << operator in a loop. At the end I want to delete the last 2 chars.

some_loop
  str << something
end
str = str[0..-3]

I think the last operation above would consume memory and time as well, but I'm not sure. I just wanted to see if there is an operation with the opposite effect of << so I can delete those 2 last chars from the same string.

Answer 1

In fact, string slicing is already a fast and memory efficient operation as the string content isn't copied until it's really necessary.

See the detailed explanation at "Seeing double: how Ruby shares string values".

Note that this is a somewhat classical optimization for string operations; You have it in java too and we often used similar tricks in C.

So, don't hesitate to do:

str = str[0..-3]

That's the correct, recommended and efficient way, provided you really have to remove those chars, see Sergio's answer.

Answer 2

Are you, by any chance, joining some array elements with a separator? Something like this?

names = ['Mary', 'John', 'Dave']

res = ''
names.each do |n|
  res << n << ', '
end

res # => 'Mary, John, Dave, '

If yes, then there's easier path.

names.join(', ') # => 'Mary, John, Dave'